1. Field of the Invention
The present invention relates to a method and apparatus for determining the density unevenness that is specific to any ink jet head.
2. Description of the Related Art
Any ink jet printer has an ink jet head that has a plurality of nozzles arranged in a line and configured to eject, for example, ink. In the ink jet printer, a recording medium is transported in a direction perpendicular to the line in which the nozzles of the ink jet head are arranged. The ink head ejects ink to the recording medium so transported, and forms an image on the recording medium. One of the various types of ink jet printers is a line head printer (i.e., one-pass line head printer), in which a recording medium is transported below the ink jet head one time, thereby to form an image on the recording medium.
In the ink jet head, the nozzles eject ink in different volumes (or amounts). That is, the amount of ink ejected from each nozzle differs that of ink ejected from any other nozzle. The difference in the amount of ink injected lowers the quality of the image formed on the recording medium in most cases. Particularly, the one-pas line heat printer may have inconvenience that results from, for example, the degrading of image quality. It is therefore useful to determine the difference between the nozzles in terms of the amount of ink ejected, in order to distinguish a good ink jet head from a defective one.
As a method of determining the difference between the nozzles of an ink jet head in terms of the amount of ink ejected, the method disclosed in, for example, Jpn. Pat. Appln. KOKAI Publication No. 2001-092966 can be utilized. The publication discloses a method of detecting streaks on a sheet-shaped object. The publication discloses an algorithm of comparing a plurality of line data items, one with another, and regarding any data item that changes more than a predetermined value, as a data time that represents an uneven streak.